1. Field of the Invention
The present invention relates to a photographing apparatus and, more particularly, to a photographing apparatus having an optical zoom function using a zoom lens, and a so-called electronic zoom function achieved by electrical processing of an image pickup means.
2. Related Background Art
Due to recent rapid spread of video cameras, the video cameras are required to have high performance, while the cameras are required to have zoom lenses having high zoom ratios, which can cope with various photographing situations. In recent years, zoom lenses having zoom ratios as high as .times.6 to .times.10 are provided, and zoom lenses having still higher zoom ratios are developed.
When a high zoom ratio is to be achieved by a zoom lens, the total length of the lens is normally increased, it becomes difficult to correct aberrations over the entire zoom area, and the cost of the lens tends to increase. For this reason, it is considerably difficult to provide a compact, low-cost zoom lens having a high zoom ratio.
In consideration of the above situation, there is proposed a technique associated with a so-called electronic zoom function for electrically enlarging an image on a monitor by processing electrical signals from an image pickup element such as a CCD, which function is added to a video camera so as to obtain a zooming effect in a wider range although the zoom ratio of an optical zoom function remains the same as a conventional one.
Japanese Patent Publication No. 52-15226 and Japanese Laid-Open Patent Application No. 1-280709 disclose techniques associated with focusing lens position control of a so-called rear-focus type zoom lens having the following advantages. That is, a zoom lens can be rendered compact by operating as a focusing lens group at least a lens group after a variable magnification lens group, and a photographing operation up to a closest object can be performed. The present invention provides a photographing apparatus, which does not adopt a simple system for operating an electronic zoom function so as to cover a wider zoom area after a zooming operation for an optical zoom area is completed, but can utilize the features of the rear-focus type zoom lens when the so-called electronic zoom function is added to the rear-focus type zoom lens.
More specifically, in the rear-focus type zoom lens, a focusing lens must be moved upon zooming even when an object remains at a position of a given distance. In particular, the rear-focus type zoom lens has an optical nature in that a focusing lens group has different focus extension amounts at the wide-angle side and the telephoto side. Therefore, in order to perform moving control of the focusing lens, as disclosed in, e.g., Japanese Laid-Open Patent Application No. 1-280709, information associated with the movement of the focusing lens is preferably stored in advance in a ROM (Read Only Memory) to move the focusing lens group according to the stored information, so that the focusing lens can trace a desirable cam path according to the lens positions of the zoom lens and the focusing lens.
In this case, the following problem is posed. That is, when the object distance abruptly changes during an optical zooming operation, the focusing lens traces a cam path for an object distance before the change, and always maintains an out-of-focus state. An AF (Auto-Focus) function may be adopted to attain an in-focus state. However, when the AF function cannot follow the zooming function, an in-focus state cannot be attained, either. In particular, a blurred state may be worsened in a zooming operation from the wide-angle side to the telephoto side even if the AF function is used.